Near rhymes:
* Squashed gear: This is a close rhyme, but it loses the headgear part.
* Squished headgear: This is another close rhyme using a similar sound.
Eye rhymes:
* Slashed headgear: This doesn't sound alike, but it looks similar on the page.
More creative options:
* Dreadful headgear: If you're going for a more metaphorical rhyme, this could work.
* Headgear, oh dear! This is playful and emphasizes the squashed nature.
Ultimately, the best rhyme depends on the context and what you're trying to achieve with your words.